1. Field of the Invention
This invention pertains to the field of polyurethane or polyisocyanurate polymers. More particularly this invention relates to use of specific polyisocyanate derivatives as a polyisocyanate source.
2. Description of the Prior Art
Polyurethane polymers such as polyurethane elastomers and foams are broadly produced by reacting an aromatic polyisocyanate and a polyol such as a polyester or polyether polyol in presence of a catalyst. Likewise, by proper choice of catalyst, polyisocyanurate polymers may be made from the same materials. Here the isocyanate groups trimerize to form the isocyanurate linkages. In many cases, the polymer may be mixed in character whereby it contains both isocyanurate groups as well as urethane linkages. By utilizing an isocyanurate group formation catalyst, the initially formed urethane quasi-prepolymer containing active isocyanate groups subsequently reacts with excess isocyanate present to form isocyanurate groups. The ultimately produced urethane-modified polyisocyanurate polymer is simply and commonly called a polyisocyanurate polymer though both groups are present. One useful class of organic polyisocyanates employed to form both polyurethanes and polyisocyanurates or mixed polymers of this type are diisocyanates.
In some instances, the diphenylmethane diisocyanates (MDI-type isocyanates) have been found to be somewhat lacking in utility. For example, it has been found that when one employs a diphenylmethane diisocyanate to prepare a flexible foam, the resultant foam quickly collapses. In other instances, the polymers formed therefrom such as in the form of elastomers, rigid foams, etc., are somewhat deficient in one or more measured physical properties of the resultant product.
It is therefore an aim of the present invention to provide a modified diphenylmethane diisocyanate which can be usefully employed in the above applications and others. It is a particular object to provide flexible polyurethanes or polyisocyanurate polymers in foam form which retain their integral character without demonstrating signs of collapse by employing modified isocyanates of this type.